This is a relatively quick and easy toddler art project that makes a burst of color for your windows.
Photo color gels -- I bought mine inexpensively on Ebay. They can be had all over the Internet at various price points. This would also be a good project for a swatchbook. Photo gels are nice for their durability in small hands, but tissue paper will do in a pinch.
Cutting tool and straight edge, or scissors
Cut your shapes. We went with triangles. Whatever's clever.
Peel your contact paper and place adhesive side up on your work surface. Ours has a faint traced pencil circle because I originally planned to affix the triangled contact paper in a wood embroidery hoop. I later abandoned that plan as unnecessary. Also, the decorated contact paper didn't really have the give to go in the hoop cooperatively.
Hand proceedings over to your small artist for decoration.
After things are arranged to suit everyone, affix another sheet of contact paper to the exposed adhesive side, sandwiching your gel shapes in between. Trim the edges as desired and enjoy your beautiful stained glass-esque masterpiece.